﻿<p>An <em>IfcCircle</em> is a curve consisting of a set of points having equal distance from the center.</p>
<blockquote class="note">NOTE&nbsp; A circular arc segment is defined by using the <em>IfcTrimmedCurve</em> with
<em>BasisCurve</em> being an <em>IfcCircle</em> or alternatively as a circular arc defined by three points within an <em>IfcIndexedPolyCurve</em>.</blockquote>

<p>Figure 2 illustrates the definition of <em>IfcCircle</em> within a three-dimensional position
coordinate system placed within the object coordinate system of an element.</p>

<table summary="example" cellpadding="2" cellspacing="2">
<tr>
<td><img src="../../../figures/ifccircle-layout1.gif" alt="axis1 placement" width="400" height="300" border="0"></td>
<td style="vertical-align:bottom; text-align:left;">
</td>
</tr>
<tr><td><p class="figure">Figure 2 &mdash; Circle layout</p></td></tr>
</table>
<p>The <em>IfcCircle</em> ia parameterized using numeric values in correspondence to the plane angle unit provided within the <em>IfcUnitAssignment</em>. If the plane angle unit is 'Degree' the parametric range of a circle is 0 &le; <em>u</em> &le; 360, if the plane angle unit is radians, the parametric range is 0 &le; <em>u</em> &le; 2&pi;.</p>
<p>&nbsp;</p>

<blockquote class="extDef">NOTE Definition according to ISO/CD 10303-42:1992<br>
A circle is defined by a radius and the location and orientation of the circle. Interpretation of data should be as
follows:
<blockquote><code style="font-size:inherit">C = SELF\IfcConic.Position.Location<br>
x = SELF\IfcConic.Position.P[1]<br>
y = SELF\IfcConic.Position.P[2]<br>
z = SELF\IfcConic.Position.P[3]<br>
R = Radius</code></blockquote>
<p style="font-size:inherit">and the circle is parameterized as</p>
<blockquote>
<blockquote><img src="../../../figures/ifccircle-math1.gif" width="205" height="22" alt="formula"></blockquote>
</blockquote>
<p style="font-size:inherit">The parameterization range is 0 &le; <em>u</em> &le; 360 degree, <em>u</em> is an angular parameter and when a numerical value is specified it shall use the current units for plane angle measure. In the placement coordinate system defined above, the circle is the equation <em>C</em> = 0, where</p>
<blockquote>
<blockquote><img src="../../../figures/ifccircle-math2.gif" width="154" height="24" alt="formula"></blockquote>
</blockquote>
<p style="font-size:inherit">The positive sense of the circle at any point is in the tangent direction, <b>T</b>, to
the curve at the point, where</p>
<blockquote>
<blockquote><img src="../../../figures/ifccircle-math3.gif" width="102" height="25" alt="formula"></blockquote>
</blockquote>
</blockquote>
<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>circle</strong> defined in ISO
10303-42</blockquote>
<blockquote class="history">HISTORY&nbsp; New entity in IFC1.0</blockquote>